1. Field of the Invention
The present invention relates to the transmission mechanism of torque and, specifically, to a flexible coupling capable of transmitting torque on a drive side smoothly and efficiently even when eccentricity occurs between the drive side and the driven side and an in-wheel motor system comprising this flexible coupling.
2. Description of the Prior Art
In a torque transmission mechanism, a rotary shaft on a drive side such as a motor and a rotary shaft on a driven side such as an impeller or a ball screw are generally connected to each other by a joint. However, it is difficult to align the drive shaft with the driven shaft in an axial direction, and a coupling 50 which is an improved version of Oldham's joint which can move in the direction of eccentricity or declination or a sliding direction as shown in FIG. 7 is used (refer to patent document 1, for example) when eccentricity or declination tends to occur between these rotary shafts. This coupling 50 comprises a hollow cylinder-like drive shaft member 52 mounted to the end of a drive shaft 51, a hollow cylinder-like driven shaft member 54 which is mounted to the end of a driven shaft 53, and a torque transmitting member 55 interposed between the above drive shaft member 52 and the driven shaft member 54. A pair of first guide members 52m and 52n made of metal are provided at the end on the driven side of the above drive shaft member 52, a pair of second guide members 54m and 54n made of metal and perpendicular to the first guide members 52m and 52n are provided at the end on the drive side of the above driven shaft member 54, first slide members 55c and 55d made of plastic are provided at the periphery of the support body 55K of the above torque transmitting member 55 in such a manner that they can slide over the inner surfaces of the above second guide members 54m and 54n, and second slide members 55a and 55b made of plastic are provided at the periphery of the support body 55K in such a manner that they can slide over the above first guide members 52m and 52n so that the above drive shaft member 52 and the above driven shaft member 54 are connected to each other in such a manner that they can move linearly in vertical and horizontal directions. Therefore, even when eccentricity or declination occurs between the drive shaft 51 and the driven shaft 53, torque can be transmitted without fail.
As a coupling having a simple structure, there is known a Schmidt coupling 60 for interconnecting a drive shaft and a driven shaft by using a link mechanism as shown in FIG. 8 (refer to patent documents 2 and 3, for example). This Schmidt coupling 60 comprises a drive-side plate 61 which turns together with a drive shaft on the same axis as the drive shaft, a driven-side plate 62 which turns together with a driven shaft on the same axis as the driven shaft and an intermediate plate 63. The above intermediate plate 63 is connected to the above drive-side plate 61 by first links 64a and 64b on one side and to the above driven-side plate 61 by second links 65a and 65b on the other side. Thereby, eccentricity between the center of the drive-side plate 61 and the center of the driven-side plate 62 is converted into the vibratory movement of the intermediate plate 63 by the first links 64a and 64b and the second links 65a and 65b, and only torque is transmitted from the drive-side plate 61 to the driven-side plate 62, thereby making it possible to transmit torque from the drive shaft to the driven shaft without fail.
Meanwhile, in a vehicle driven by a motor, such as an electric motor, in-wheel motor systems incorporating a motor in a wheel are being employed. Out of these, there is proposed an in-wheel motor system in which the stator side of a hollow direct drive motor 3 installed in a wheel portion is supported to a part around the wheel of a vehicle by an elastic body and/or an attenuation mechanism and the motor 3 is float-mounted to the part around the wheel to make the motor 3 function as the weight of a dynamic damper (refer to patent document 4, for example). Thereby, ground contact performance and riding comfort while driving on a rough road can be both greatly improved.
In this in-wheel motor system, stated more specifically, a non-rotating side case 3a supporting a stator 3S is elastically supported to a knuckle 5 which is a part around the wheel of a vehicle by a buffer mechanism 30 comprising two plates 34 and 35 which are interconnected by springs 32 and a damper 33 moving in the vertical direction of the vehicle and whose moving directions are limited to the vertical direction of the vehicle by direct-acting guides 31, and a rotating side case 3b supporting a rotor 3R and a wheel 2 are interconnected by a flexible coupling 40 as a drive force transmitting mechanism which can be eccentric in the radial direction from the wheel 2. The above flexible coupling 40 comprises a plurality of hollow disk-like plates 41A to 41C and direct-acting guides 42A and 42B for interconnecting adjacent plates 41A and 41B and adjacent plates 41B and 41C and guiding the adjacent plates 41A and 41B and the adjacent plates 41B and 41C in the radial direction of the disk as shown in FIG. 10. The in-wheel motor 3 can move in the moving direction of the above direct-acting guides 42A and 42B, that is, the radial direction of the disk but not in the rotational direction, thereby making it possible to transmit drive torque from the motor 3 to the wheel 2 efficiently.
Patent document 1: Japanese Laid-open Patent Application No. 9-269013
Patent document 2: Japanese Laid-open Patent Application No. 49-78050
Patent document 3: Japanese Laid-open Patent Application No. 9-267243
Patent document 4: WO 02/083446 A1